Mask blanks are used in machining tools for manufacturing integrated circuits in order to serve as an exposure mask for example in a stepper device. Usually, a mask blank comprises a carrier device, preferably made of glass having a thickness of about 6 mm, to which is applied a molybdenum-silicon nitride layer preferably having a thickness of 100 nm and, over the latter, a chromium layer likewise having a thickness of 100 nm as hard mask. Arranged above that is a photoresist layer having a thickness of 500 nm, for example.
In order to be able to serve as a patterned mask, the mask blank or the layers deposited on the glass must be patterned in various machining steps. This patterning is effected for example in pattern generators. For this purpose, the mask blank is quite generally clamped in a fixing or clamping device. Customary clamping devices clamp a mask blank by means of mechanical spring elements. This often leads to mechanical stresses or flexures of the mask blank and thus to a reduced quality of the patterned mask.
Hitherto, such dislocations and strains have only been detected or identified at the end of the process for producing the mask blank or the mask in the form of registration fluctuations, accuracy or position fluctuations and other faults. Mask blanks which lie outside a tolerance range have to be separated out by sorting.